Mayor Michael Nutter told ABC News that officials were confident there were no more people buried beneath the rubble where the four-story building collapsed on Wednesday morning, falling on top of a two-story building that housed a Salvation Army thrift store.

The search-and-rescue operation lasted 30 hours.

Officials released the identities of the people who were killed: Kimberly Finnegan, Borbor Davis, Anne Bryan, Juanita Harmin, Mary Simpson and Roseline Conteh.

Family and friends of Finnegan, who was 35, Davis, who was 68, and Bryan, who was 24, have all released statements about the deaths. All three were in the Salvation Army when the building next door fell.

Finnegan's friend, Heather Sizemore, told ABC News affiliate WPVI, "She was a fiancee and a good friend to a lot of people, and a good person."

Davis's wife, Maggy, described her husband as "quiet and kind."

"He goes to work every day," she said. "He never misses a day."

The Philadelphia Academy of Fine Arts, where Bryan was a first-year student, released a statement from her family that said she was "brilliant and caring."

"An extremely talented artist, Anne possessed a passion for the arts and an ability to find beauty in everything around her," the family said in the statement. "That she will not be here to continue to touch the lives of those around her is of intense pain to all of our family and her friends. This pain is fresh and it runs deep."

The Salvation Army released a statement today saying that two of the deceased were Salvation Army employees, and that the organization was working closely with Philadelphia officials and providing support to the victims' families.

"We are deeply saddened by the tragic loss of life of the six individuals who perished in the wake of yesterday's building collapse," the statement said. "The passing of these individuals, including two of our employees, will be felt across our entire organization and throughout the community."

Of the 14 people extricated from the debris, many have been treated and released from area hospitals with minor injuries, according to hospital officials. At least one victim, 61-year-old Myra Plekam, remains in critical condition at the University of Pennsylvania after she was pulled Wednesday evening from the rubble.

Philadelphia officials faced tough questions earlier today over whether the building collapse could have been prevented.

Nutter and the city's commissioner of licenses and inspections, Carlton Williams, said today that complaints about the working conditions at the Center City demolition site were not followed up on.

City officials said that a routine inspection had found no violations at the property before demolition began. Williams said that inspectors had visited an adjoining property in May after complaints were lodged, but they found no violations and did not return to the Market Street site before Wednesday.

"No subsequent inspection occurred to indicate there was any unsafe conditions," Williams said. "We did not follow up and we are definitely looking into that."

Nutter promised a "wide-ranging investigation" into how and why the building collapsed.

"We are 24 hours into the incident and we have a lot of work to do into why it happened and how did it happen, and, going forward, [to find out] how to prevent it from happening anywhere else in the city," Nutter said today.

Nutter and Williams made their statements in response to questions from reporters about a slew of complaints and 311 calls that had reportedly been made to the city about the unsafe conditions at the site in the weeks leading up to the collapse.

At least 20 people were caught in falling debris when the building collapsed Wednesday around 10:45 a.m. An outer wall of the building that was being demolished fell outward and onto the two-story building, according to city officials.

Fourteen people were treated for injuries, most of which were minor, according to hospital officials. Six had already died by the time rescuers found them in the rubble.

During the search on Wednesday, rescue workers detected cell phone signals that led them to believe there were additional people buried after the first 14 people were pulled out. They searched for cell phone signals in the debris to find additional people, according to Nutter's office.

Two construction workers that were doing work on nearby buildings told the Philadelphia Inquirer today that they watched the demolition in disbelief because of the unsafe practices of the demolition workers.

"Never in all my years have I ever, ever, ever seen this," Steve Cramer told the paper. "It was just a total disregard for safety. We [predicted] this last week. I can't believe they allowed the thrift store to be open."

Joe Hauser, another worker, echoed Cramer's concerns, saying that he was planning on saying something to the workers on the very day of the collapse.

"I said, 'That's it, at lunch I'm going to go over there and say something, I have to, I can't go with this no more,'" Hauser told the paper.

On Wednesday, Williams and Nutter said that the building had up-to-date permits for the demolition, noting that both the owner and construction company had their paperwork in order.

The property's owner, STB Investments of New York City, released a statement Wednesday expressing sympathy for the victims.

Richard Basciano, an owner of the company, owned many properties in Philadelphia and New York and was once dubbed "the undisputed king of Times Square porn" in New York newspapers because of his ownership of adult businesses.

"Our thoughts and prayers go out to the people affected by this tragic event. Please know that we are committed to working with the City of Philadelphia and other authorities to determine what happened today," the statement read.